This invention relates to semiconductor device packages and the method of making such packages and more specifically relates to a chip-scale package and method of its manufacture.
Semiconductor device packages are well known for housing and protecting semiconductor die and for providing output connections to the die electrodes. Commonly, the semiconductor die are diced from a large parent wafer in which the die diffusions and metallizing are made in conventional wafer processing equipment. Such die may be diodes, field effect transistors, thyristors and the like. The die are fragile and the die surfaces must be protected from external environment. Further, convenient leads must be connected to the die electrodes for connection of the die in electrical circuits.
Commonly, such die are singulated from the wafer, as by sawing, and the bottom of the die is mounted on and connected to a portion of a lead frame which has identical sections to receive respective die. The top electrodes of the die are then commonly wire bonded to other portions of the lead frame, and a molded insulation housing is then formed over each lead frame section enclosing the die, and permitting lead portions of the lead frame to penetrate through the molded housing to be available for external connection.
It is desirable in many applications that packaged semiconductor devices be as small as possible to enable the mounting of many such devices on a support surface, such as a printed circuit board or an IMS (insulation-metal-substrate) support surface. Devices housed in the conventional manner occupy a much larger area than the area of the die which is housed. It would be very desirable to provide a semiconductor package which offers the same purposes of the conventional housing (of protecting the die and providing convenient external connection to the die electrodes), but which will occupy less surface area on a support surface.
This invention provides a novel semiconductor die package of xe2x80x9cchip-scalexe2x80x9d. That is, the package of the present invention occupies very little more area than the actual area of the die. Thus, the invention reduces the package area (or xe2x80x9cfootprintxe2x80x9d) to close to the irreducible area of the die itself. The invention also provides a novel process for forming such chip-scale packages.
In accordance with the present invention semiconductor die are first processed in conventional wafer form. The completed semiconductor wafer is then bonded to a bottom contact wafer which is preferably made of a metal having thermal expansion characteristics similar to those of silicon, and, typically may be of molybdenum or tungsten. In this bonding process, the die bottom will have a bottom electrode of any suitable metal and is preferably overcoated with silver. Similarly, the base contact plate or wafer preferably has a metallized (silver) surface. Thus, the bottom surface of the silicon wafer and top surface of the base contact can be connected by diffusion bonding, soldering, eutectic bonding or the like.
The top contact wafer is similarly of a material having thermal expansion characteristics matched to that of silicon and its bottom surface can be metallized with silver, matching the metallized top surface of the electrode, or electrodes, on the die wafer surface.
The top contact is further processed so that the contact sections for each die location are pre-cut to define separate contact portions when the devices are singulated. The separated cuts are filled in with a suitable plastic such as an epoxy or polyamide. A bottom groove in the top contact is filled with a plastic filler also encloses respective device areas and defines a thinned area.
The top metal wafer and base metal wafer are then bonded to the silicon die wafer in a common bonding or soldering operation, with the top electrode contacts aligning with and contacting the contact areas of the respective die.
The bonded assembly is then saw-cut to singulate each die (in the conventional die streets) with its respective top and base contacts covering the full top and bottom die area. The die junctions are well protected and wire bond or pressure connections can be easily made to the top and bottom contacts.